The present invention relates to an inkjet printer containing a substantially closed ink duct and a transducer that is substantially parallel to the closed duct, this transducer deforming by actuation in order to generate a pressure wave in the duct.
An inkjet printer of this kind is known from U.S. Pat. No. 4,688,048. As is known from the prior art, actuation of a transducer of the above kind causes it to deform, so that a sudden volume change occurs in the duct (also referred to as “ink chamber”). This produces a pressure wave in the duct. If the pressure wave is strong enough, this leads to a drop of ink being ejected from the duct nozzle. In this manner, each individual actuation may lead to a drop of ink being ejected. By imposing such actuations image-wise, an image, built up of individual ink drops, can be formed on a receiving medium. It is known from said patent, that the generated pressure wave comprises first, second, third, fourth and higher order harmonics. Depending on the size of the transducer and position relative to the duct, generally one of said harmonics is handled. A typical drop size is associated with each harmonic, where the size decreases in line with a higher order harmonic generally being handled. In order to handle, for example, a third order harmonic (see FIG. 3 of said U.S. patent) it may be opted to use a transducer the length of which is equal to one third of the duct length, this transducer coinciding with the antinode of this harmonic. In order to handle a higher order harmonic, it may also be opted to use two or more separate transducers (see FIG. 6 of said U.S. patent), the position of which coincides with antinodes of this higher order harmonic. This known method is suitable for handling higher order vibrations very selectively and, as a result, to generate drops with a very small volume, without this requiring for the size of the exit opening to be reduced and/or the drop speed to be modified.
However, the known printer does have major disadvantages. If it is opted to apply one transducer, the position of which coincides exactly with the antinode of a higher order harmonic, then this transducer will at all times only be able to extend along the limited length of the duct. The higher the order of the desired harmonic, the shorter the length of the transducer will be. In order to achieve a strong enough volume change in the duct using such a small transducer, a relatively high actuation voltage will be required. High voltages reduce the lifespan of the transducer and therefore that of the printhead. Furthermore, it will be virtually impossible for fourth or higher order vibrations to obtain large enough volume changes using one transducer. In these cases, it will therefore be necessary to opt for the application of two or more individually actuatable transducers. The disadvantage of this approach is that it leads at least to duplication of the actuation electronics of the printheads. Furthermore, the application of two or more individually actuatable transducers will make the production of the printheads much more complex. Therefore, the application of two or more individual transducers per ink duct, although repeatedly referred to in the patent literature (see for example DE 43 28 433, JP 60 011369, U.S. Pat. No. 4,672,398) is not financially attractive.